1. Field of the Invention
The present invention relates to a surface light source having flat exit surfaces on its upper and lower surfaces and a double-sided display device using the light source.
2. Description of the Related Art
As a surface light source having a flat exit surface, a light source is known, which has a light-emitting element and a light guide plate which allows light emitted from the light-emitting element to be incident from an end face, and causes the light to emerge from the front surface.
Conventionally, a surface light source of this type is comprised of a light guide plate which is formed from a transparent plate such as an acrylic resin plate and has one end face on which a light from a light source is incident, a front surface from which light transmitted through the transparent plate emerges, and a reflecting film formed on an entire rear surface facing the front surface of the transparent plate, and a light-emitting element serving as the light source formed from an LED (Light-Emitting Diode), cold cathode tube, or the like.
In this surface light source, light emitted from the light-emitting element and incident on the light guide plate from the incident end face is guided in the light guide plate while repeating internal reflection of the light by the front surface of the light guide plate and reflection of the light by the rear surface of the light guide plate, and the light finally emerges from the front surface.
The above surface light source is used as an illumination light source for a display device such as a liquid crystal display device. In a display device of this type, a display element which performs display by controlling transmission of light is placed on the front side of the surface light source such that the observation surface of display faces the opposite side to the surface light source.
Recently, as electronic equipment such as a cell phone or portable terminal device having a lid that can open and close with respect to an equipment body, an electronic equipment has appeared, which has display sections on the inner surface (the surface that faces the equipment body when the lid is closed) and the outer surface so as to be capable of displaying information while the lid is open and closed.
A conventional surface light source is designed to make light emerge to only the front side. In order to manufacture the electronic equipment having display sections on the two surfaces, therefore, surface light sources must be placed on the respective display sections.